Round 1 is my favourite of all the MCN events, there's some really nasty steep descents - especially coming down to the Llanthony CP. it's boggy/muddy up on the second half and last year the final section was a complet mud fest.
I used Inov8 x-talons and was glad I did, if it's dry for the next month, (ha ha ha) you might get away with something less aggressive.
I've done Round 1 three times, and the weather has been epic each time - snow, hail, gales, rain, mud, bogs etc... don't skimp on kit - you have been warned
I signed-up yesterday for the marathon so there's still places left. My 3rd time at Pompey - you can park on-street a couple of hundred yards away from the Pyramids for free, I've never had any problems finding a space
I keep looking into buying a treadmill http://www.fitness-superstore.co.uk/ have some great deals, a chap at work has recently bought one for £600 on interest free credit, (£20/month) and raves about it.
BUT - I have a gym membership at PureGym that is £16.99/month for life and 15 minutes walk from my house. £600 is 3 years of gym membership at that price.
There's lots of cheap 24-hour gyms around at the moment, PureGym, EasyGym, TheGym etc... Probably a much better option